Rotary shafts such as rotary driveshafts, propeller shafts, and crankshafts are often used in the power train and engine designs of modern automotive vehicles. Rotary driveshafts are used to drive the front wheels of front wheel driven vehicles, propeller shafts are used to drive the rear drive system in rear wheel driven vehicles, and crankshafts are used to transmit power from the engine to the power train. In studying the rotational movement of such rotary shafts, it is known that certain unbalanced rotation may occur at certain rotational speeds or due to uneven power input thereby causing undesirable vibrations. These undesirable vibrations often present themselves as bending and torsional forces within the shaft during rotation.
For many years, this problem has been recognized and a variety of devices have been constructed and used to lessen or dampen the resultant vibrations. One common form of a damper comprises an inner metal hub attached to a rotary shaft, an outer metal annular member or “inertia member”, and an elastomer member positioned under compression between the hub and outer member. The hub directly executes the vibrations created by the shaft due to its rigid coupling thereto. The inertia member is coupled to the hub by the elastomer member and accordingly causes a phase lag between the oscillations of the hub and the corresponding oscillations of the inertia member thereby reducing or eliminating vibrations in the shaft.
Such dampers are designed or “tuned” to generate a prescribed vibrational frequency adjusted to the dominant frequency of the excited harmful vibrations. The damper converts or transfers the vibrational energy of the rotary driveshaft to the damper by resonance, and eventually absorbs the vibrational energy of the rotary driveshaft. In short, the damper attempts to cancel or negate vibrations that are induced onto or caused by the rotary driveshaft in normal operation of the drive train of the vehicle.
Elastomer members used in such known dampers exhibit a set part frequency based upon their rubber hardness and thickness. In the manufacture of such dampers, sometimes the part frequency needs to be lower than what can be achieved with the typical softest rubber compounds used in a typical sheet-like geometry. Therefore, there is a need in the art to develop an elastomer element that achieves lower part frequency independent of its composition or based primarily on its part geometry.